FU LIXIN, emotionally exhausted from caring for her sick mother, needed a little pick-me-up. A friend offered her a "special cigarette" – one laced with methamphetamine – and she happily inhaled.
The next day, three policemen showed up at her door. "They asked me to urinate in a cup," Fu said. "My friend had been arrested and turned me in. It was a drug test. I failed on the spot."

Although she said it was her first time smoking the drug, Fu, 41, was sent to one of China's compulsory drug rehabilitation centres. The minimum stay is two years, and life is an unremitting gauntlet of physical abuse and forced labour without any drug treatment, according to former inmates and substance abuse professionals. "It was a hell I'm still trying to recover from," she said.

According to the United Nations, up to half a million Chinese citizens are held at these centres at any given time. Detentions are meted out by the police without trial.

Now international human rights activists are stepping up opposition to the centres.

Created in 2008 as part of a reform effort to grapple with the country's growing narcotics problem, the centres have become de facto penal colonies where inmates are sent to factories and farms, fed substandard food and denied basic medical care, lawyers and drugs, experts have claimed.

"They call them detoxification centres, but everyone knows that detox takes a few days, not two years," said Joseph Amon, an epidemiologist with Human Rights Watch in New York. "The basic concept is inhumane and flawed."

Last week Human Rights Watch issued a report on the drug rehabilitation system that replaced the Communist Party's previous approach of sending addicts to labour camps, where they would toil alongside thieves, prostitutes and political dissidents.

The report, Where Darkness Knows No Limits, calls on the government to immediately shut the centres. Under the Anti-Drug Law of 2008, drug offenders were to be sent to professionally staffed detox facilities and then released to community-based rehabilitation centres for up to four years of therapeutic follow-up.

But substance abuse experts claim the legislation has simply given the old system a new name. What is worse, they say, it expands the six-month compulsory detentions into two-year periods the authorities can extend by five years.

Wang Xiaoguang, vice-director of Daytop, a US-affiliated drug-treatment residence in Yunnan Province, said the government detox centres were little more than business ventures run by the police. Detainees, he said, spend their days working at chicken farms or shoe factories which have contracts with the local police. Drug treatment and counselling are almost nonexistent.

"I don't think this is the ideal situation for people trying to recover from addiction," Wang said. In its report, Human Rights Watch, which largely focused on Yunnan, says the abuses at some of the province's 114 detention centres are even more troubling. Those with serious illnesses, including TB and Aids, are often denied medical treatment. Many inmates reported beatings, some fatal.

Han Wei, 38, a recovering heroin addict released from a Beijing detention centre in October, said the guards would use electric prods.

Meals consisted of steamed buns and, occasionally, cabbage-based swill. Showers were allowed once a month. And the remedy for heroin withdrawal symptoms was a pail of cold water in the face. "They didn't give me a single pill or a bit of counselling," Han said.

Despite the deprivations, Han, a former nightclub owner, said his two-year sentence persuaded him to kick a habit he began in 1998. "I'm never going back," he said.

Zhang Wenjun, who runs Guiding Star, an organisation that helps recovering addicts, said such determination was most often fleeting. At least 98 per cent of those who leave the drug detention system relapse within a few years, he said.

Zhang's own heroin addiction has landed him in detox centres and labour camps six times since the mid-1990s. "What the government doesn't realise is this is a disease that needs to be treated, not punished," said Zhang, 42.

In some ways, he said, the stigma of addiction is as crippling as the lure of the next fix. Those arrested are branded addicts on their national identification cards, which makes applying for jobs and benefits futile. And because the local police are automatically notified when former offenders check into hotels, travelling often involves impromptu urine tests and the possibility of humiliation in front of colleagues. "In China, to be a drug addict is to be an enemy of the government," Zhang said.

However, he and other drug treatment workers are quick to acknowledge the progress that China has made in recent years. There are now eight methadone clinics in Beijing, serving 2,000 people, and more than 1,000 needle-exchange programmes have opened across the country since 2004.

Yu Jingtao, whose organisation, Beijing Harm Reduction Group, distributes 30,000 clean needles a month, said the government was slowly moving towards the drug treatment model common in much of the developed world. "We're just caught in a transition period," said Yu, himself a recovering addict. "Transition periods are never very pretty."